#include <iostream>
#include "math.h"
#include "glad/glad.h"
#include "GLFW/glfw3.h"
#include "shader/Shader.h"

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void processInput(GLFWwindow *window);

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

int main()
{
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

#ifdef __APPLE__
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
#endif

   // glfw window creation
    // --------------------
    GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
    if (window == NULL)
    {
        std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);

    // glad: load all OpenGL function pointers
    // ---------------------------------------
    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
    {
        std::cout << "Failed to initialize GLAD" << std::endl;
        return -1;
    }

    //创建Shader
    Shader ourShader("./res/shaders/shaderTriangleFlip.vs", "./res/shaders/shader.fs");

    //三角形坐标
    float vertices[] = {
        // 位置              // 颜色
         0.5f, -0.5f, 0.0f,  1.0f, 0.0f, 0.0f,   // 右下
        -0.5f, -0.5f, 0.0f,  0.0f, 1.0f, 0.0f,   // 左下
         0.0f,  0.5f, 0.0f,  0.0f, 0.0f, 1.0f    // 顶部
    };

    //顶点数组对象，顶点属性调用都会储存在这个VAO中
    GLuint VAO;//vertex array object
    glGenVertexArrays(1, &VAO);
    glBindVertexArray(VAO);

    //顶点缓冲对象，一次性发送多个顶点对象到GPU
    GLuint VBO;// vertex buffer object
    glGenBuffers(1, &VBO);
    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);    

    //如何解析顶点数据
    //param1 shader中location对应的0
    //param2 顶点个数 3个（坐标，颜色）
    //param3 顶点数据类型 float
    //param4 是否归一化
    //param5 步长，6（坐标3个顶点，颜色3个顶点） * sizeof(float)，下一个顶点位置
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GL_FLOAT), (void*)0);
    glEnableVertexAttribArray(0);

    //颜色
    //param1 shader中location对应的1
    glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 6 * sizeof(GL_FLOAT), (void*)(3 * sizeof(GL_FLOAT)));
    glEnableVertexAttribArray(1);


    // render loop
    // -----------
    while (!glfwWindowShouldClose(window))
    {
        // input
        // -----
        processInput(window);

        // render
        // ------  
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
      
        //画自定义 
        ourShader.use();

        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 6);        

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glDeleteVertexArrays(1, &VAO);
    glDeleteBuffers(1, &VBO);    

    // glfw: terminate, clearing all previously allocated GLFW resources.
    // ------------------------------------------------------------------
    glfwTerminate();
    return 0;
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void processInput(GLFWwindow *window)
{
    if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
    // make sure the viewport matches the new window dimensions; note that width and 
    // height will be significantly larger than specified on retina displays.
    glViewport(0, 0, width, height);
}